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Graphical abstract Highlights • Copper (I) complexes containing pyridine-imidazole ligands were synthesized. • Different substituents such as bromide, methyl, and phenyl groups were functionalized onto the pyridine ring. • Efficient green-yellow emission was achieved with emission wavelength of 547–569 nm and quantum yields of 24.8–53.0%. • DFT and TDDFT methods were employed to explain the experimental results. Abstract A series of the pyridine-imidazole (PyIm) Cu(I) complexes with different substituents (bromide (P1), methyl (P2), and phenyl (P3)) attached on the pyridine ring are synthesized and characterized. All the complexes show the typical metal-to-ligand charge transfer (MLCT) absorption in the visible region. Complex P1 with an electron-withdrawing substituent on the pyridine ring, e.g., a bromine group, shows a red shift of the emission wavelength. Conversely, an electron-donating substituent on the pyridine ring in complex P2 , e.g., a methyl group, shifts the emission to longer wavelength. Similarly, complex P3 containing the extended π-conjugation system of the ligand also exhibits a red shift of the emission wavelength. All of the complexes exhibit efficient green-yellow emission in PMMA films at room temperature with emission wavelength of 547–569 nm and quantum yields of 24.8–53.0%. Meanwhile, DFT and TDDFT methods were employed to explain the photophysical properties. [ABSTRACT FROM AUTHOR]

Three four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes, [Cu(Py-Im)(POP)](PF6) (P1), [Cu(Py-BenIm)(POP)](PF6) (P2), and [Cu(Py-c-BenIm)(POP)](PF6) (P3) (Py-Im = 3-methyl-1-(pyridin-2-yl)-1H-imidazolylidene, Py-BenIm = 3-methyl-1-(pyridin-2-yl)-1H-benzo[d]imidazolylidene, Py-c-BenIm = 3-methyl-1-(pyridin-2-ylmethyl)-1H-benzo[d]imidazolylidene, POP = bis([2-diphenylphosphino]-phenyl)ether), have been synthesized without transmetalation of the NHC–Ag(I) complex for the first time. The photophysical properties of the resultant NHC–Cu(I) complexes have been systematically investigated via spectroscopic methods. All complexes exhibit good photoluminescence properties with long excited-state lifetimes and moderate quantum yields. Density functional theory and time dependent density functional theory calculations were employed to rationalize the photophysical properties of the NHC–Cu(I) complexes. [ABSTRACT FROM AUTHOR]

• Four-coordinate N-heterocyclic carbene (NHC) Cu(I) complexes bearing different diphosphine ligands are synthesized and characterized. • The photophysical properties of the resulting complexes is investigated. • Complexes show yellow-green emission in 525–555 nm region with the phosphorescent origin. • The differences of the photophysical properties were rationalized by DFT and TDDFT calculations. Here, we report a series of the four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes having the same bidenate NHC ligand and different bisphosphine (P^P) ligands, [Cu(CNbenPy-benzIm)(Naphphos)]PF 6 (P1), [Cu(CNbenPy-benzIm)(cyc-xantphos)]PF 6 (P2), and [Cu(CNbenPy-benzIm)(xantphos)]PF 6 (P3), (CNbenPy-benzIm = 3-(3-cyanobenzyl)-1-(5-phenylpyridin-2-yl)-1 H -imidazolylidene; BINAP = 2,2′-bis(diphenylphosphino)-1,1′-binaphthalene; cyc-xantphos = (9,9-dimethyl-9 H -xanthene-4,5-diyl)bis(dicyclohexylphosphine), xantphos = 9,9-dimethyl-9 H -xanthene-4,5-diyl)bis(diphenylphosphine)). P1 exhibits the metal-to-ligand charge transfer (MLCT) absorption band at 366 nm with high molar extinction coefficient of 2.44 × 104 M−1 cm−1, while P2 and P3 show a blue-shift of the MLCT absorption band at 336–341 nm with the molar extinction coefficients of 0.82–1.16 × 104 M−1 cm−1, which are just a little lower than that of P1. The emission wavelengths of all NHC-Cu(I) complexes can be fine-tuned to cover the spectral range of 525–555 nm with the phosphorescent origin in PMMA films. P1 has the lowest photoluminescence efficiency of 5.50% with the red-shifted emission wavelength at 555 nm and the emission lifetime of 237 μs, whereas P3 show the highest photoluminescence efficiency of 39.5% with the blue-shifted emission wavelength at 525 nm and the emission lifetime of 64.4 μs. The differences for photophysical properties of NHC-Cu(I) complexes were rationalized using density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. [Display omitted] [ABSTRACT FROM AUTHOR]

• Three-coordinate copper(I) complexes bearing POP and monodentate substituted-quinoline ligands were synthesized and characterized. • The electron-donating/withdrawing groups including methoxyphenyl and trifluoromethylphenyl groups were inserted into the complexes. • Cu(I) complexes exhibited yellow-green emissions at 542-558 nm with longer excited-state lifetimes of 179–487 µs. • The photophysical properties were explained by DFT and TDDFT calculations. The three-coordinate Cu(I) complexes [Cu(POP)(X)]PF 6 , X = quinoline (P1), 2-(4-methoxyphenyl)quinoline (P2), 2-(4-(trifluoromethyl)phenyl)quinoline (P3), POP = bis[(2-diphenylphosphino)phenyl] ether were synthesized and characterized. The photophysical properties of these Cu(I) complexes were tuned by the addition of organic groups including methoxyphenyl and trifluoromethylphenyl groups into the quinoline ligand. The resulting complexes exhibit the metal-to-ligand charge transfer (MLCT) band in the lower energy. The emissions for all the complexes in solid state are in the range of 542–558 nm with higher quantum yields of 11.4–14.2% and long-lived excited lifetimes of 179–481 µs at room temperature. The photophysical properties were further explained by DFT and TDDFT methods. [Display omitted] [ABSTRACT FROM AUTHOR]

• Schiff base copper (I) complexes bearing the bulky adamantyl moiety were synthesized and characterized. • The electron-donating/withdrawing groups including –OCH 3 and –CF 3 were inserted into the complexes. • Cu(I) omplexes exhibited organe-red emissions at 611–619 nm with shorter excited-state lifetimes of 5.55–7.53 μs. • The origin of the emission is attributed the 3MLCT/3LLCT/3π-π* state supported by the TDDFT calculations. Herein, the three novel copper (I) complexes bearing Schiff base ligands of the types [Cu(Phen-PyMethylene-Adam-Amine)(POP)]PF6 (P1), [Cu(Methoxyl-Phen-PyMethylene-Adam-Amine)(POP)]PF6 (P2), and [Cu(TriflMethyl-Phen-PyMethylene-Adam-Amine)(POP)]PF6 (P3) (Phen-PyMethylene-Adam-Amine = ((5-phenylpyridin-2-yl)methylene)adamantan-1-amie, Methoxyl-Phen-PyMethylene-Adam-Amine = ((5-(4-methoxyphenyl)pyridin-2-yl)methylene)adamantan-1-amine, TriflMethyl-Phen-PyMethylene-Adam-Amine = ((5-(4-(trifluoromethyl)phenyl)pyridin-2-yl)methylene)adamantan-1-amine, POP=bis[2- diphenylphosphino ]-phenyl)ether) have been prepared and investigated. Incorporation of the bulky adamantyl group into the complexes can enhance the stability of the complexes. The different electron-donating/withdrawing groups such as –H, –OCH 3 , and –CF 3 substituents were functionalized onto the pyridine ring part of Schiff base ligands to tune the emission behavior of the resulting Schiff base Cu(I) complexes. All complexes exhibit the lowest energy metal-to-ligand charge transfer (MLCT) characters in 400–450 nm region showing a slight blue-shift of the absorption wavelengths in the order P3 > P1 > P2. Organe-red emissions in the region of 611-619 nm with photoluminescence quantum yields (PLQY) of 1.0–1.3% can be observed in the solid state. Additionally, the photophysical properties are also investigated theoretically using density functional theory (DFT) and time dependent DFT. [Display omitted] [ABSTRACT FROM AUTHOR]